(1) Field of the Invention
The present invention relates to a low NO.sub.x level combustion method in a radiant tube burner and to a combustion apparatus used for the method, and provides a technic for suppressing the generation of NO.sub.x by carrying out a smooth two-stage combustion in the interior of a radiant tube.
(2) Description of the Prior Art
In general, when a fuel gas is burnt by a burner arranged in a radiant tube used in an annealing installation, a high load combustion must be carried out in a narrow tube, and therefore the combustion by the burner in the radiant tube has a drawback that the amount of NO.sub.x gas generated in the combustion by the radiant tube burner is larger than the amount of NO.sub.x gas generated in the combustion by an ordinary industrial furnace, wherein fuel is burnt in a large space. Moreover, it is difficult to decrease the NO.sub.x level in a radiant tube burner by merely applying a low NO.sub.x level combustion means used in an ordinary industrial furnace to the radiant tube burner, and further it is difficult to produce a nozzle which is adapted to be used in a small-diameter radiant tube and has a structure for carrying out a low NO.sub.x level combustion. Accordingly, low NO.sub.x level combustion can not substantially be attained by merely modifying the burner structure in the radiant tube, and indeed there has never been known a radiant tube burner capable of attaining a satisfactorily low NO.sub.x level combustion.